The objective of this project was to create an independent WSPR beacon transmitter.  As such it should operate completely independently – no computer in the shack, no internet time server and no power from the grid.

 

I found that a U3S kit + GPS kit both from QRP Labs met my requirements for a transmitter with internal controller, GPS disciplined frequency synthesizer and GPS timing.  WSPR operates on 2 minute time segments and timingGPS + U3S must be accurate to a very few seconds or no one will be able to decode your transmission.  Similarly the frequency band for WSPR signals is only a few hundred Hz wide, so if your frequency is not exact;  no reception.

 

The photo at left shows the transmitter (bottom of the box) and GPS (top shelf) mounted in a weatherproof PVC electrical box.  The box is mounted on a steel plate, that allows the assembly to be attached to the 2″ pipe mast with U bolts.  (This transmitter puts out approximately 500 mW on 30m with a 25% duty cycle — 2 minutes on, 6 minutes off; the antenna is a dipole with the mast providing the center support.)

temporary panel installation

 

After getting the transmitter and GPS to work successfully inside the shack, I started my quest for independent power.  I started with a 5W solar panel and a 7 AH gel cell battery.  The 12V battery voltage is knocked down to 5 V for the transmitter using a low cost buck regulator module (internet shopping).  In the photo above, the smaller 5W solar panel is shown on the left hand chair next to the newer 10W panel that eventually came in the mail.  The charge regulator is on the right hand chair just in front of the battery.  This arrangement was almost good enough so I sprung for a larger, 12 AH battery.  The 10 W panel and the 12 AH battery easily carried the transmitter through the night until the morning sun could re-start the charge cycle.

mounting bracket clamped together

So it was time to fabricate a bracket that would hold the solar panel on the mast.  I wanted the bracket to be adjustable so I put a leaf hinge at the top.  The mounting holds the panel at an angle by moving the support arm from one hole to another.  A position for any season.

I used 2 mm mild steel plate for the bracket.  The solar panel is held in place by aluminum U channel that was left over from my main antenna tower project.  I believe that suitable aluminum profiles should be available from any aluminum window manufacturer.  I took considerable care positioning the plates and the hinge before welding it together.  After I cleaned up my welds and removed as much rust as possible from the plates I gave them a coat of galvanizing spray followed by blacSAM_2401 croppedk enamel spray.

I originally intended putting the gel cell battery in the lower PVC box.  After I determined that I needed a larger capacity battery I used this box for the charge controller and the 5 V buck regulator.  The 1.8W Canadian Tire panel shown on the right was not used in the final system.

The 12 AH battery is sitting on the ground inside a plastic box from the Dollar Store and weighted down with a brick.  I will eventually get round to something more elegant, but it does work.

The whole system has been up and running 24/7 for some days now and appears stable.

You can see the WSPR beacons by going to http://wsprnet.org/drupal/wsprnet/map

Select the 30m map and a time period of 30 minutes. Click on any station call sign to see who is hearing who.

 

 

In summary I will list the components or modules I found suitable for making an independent power system:

  • Solar panel of sufficient power rating
  • Battery with sufficient storage capacity
  • Charge regulator
  • Regulator to drop the battery voltage down to that required by the circuits being powered (if necessary)solar panel with transmitter
  • Weatherproof boxes
  • Sturdy mounting system

 

Some possible applications:

  • repeaters
  • beacons
  • remote antenna tuners